fix(unity): treat a MonoBehaviour with a missing script as classless

src/nnnotes/unity.py

@@ -327,18 +327,23 @@ def _head_node(node: TypeTreeNode) -> TypeTreeNode | None:
     return head
 
 
-def script_class(obj) -> str:
-    """Class name of a MonoBehaviour (needs the monoscript bundle loaded). Reads the header up to m_Script with the
-    object's own typetree (not its fields); the whole object when that is not possible."""
+def script_class(obj) -> str | None:
+    """Class name of a MonoBehaviour (needs the monoscript bundle loaded); None for a missing script (null m_Script).
+    Reads the header up to m_Script with the object's own typetree (not its fields); the whole object when that is
+    not possible."""
     try:
         head = _head_node(obj._get_typetree_node())
         if head is not None:
-            ms = deref(obj, obj.read_typetree(head, check_read=False)["m_Script"])
-            if ms is not None:
-                return ms.read().m_ClassName
+            pptr = obj.read_typetree(head, check_read=False)["m_Script"]
+            if not pptr["m_PathID"]:
+                return None
+            return deref(obj, pptr).read().m_ClassName
     except Exception:
         pass
-    return obj.read().m_Script.read().m_ClassName
+    script = obj.read().m_Script
+    if not script.m_PathID:
+        return None
+    return script.read().m_ClassName
 
 
 def strip_pptrs(tt: dict) -> dict:

tests/test_speed_exact.py

@@ -137,6 +137,19 @@ def test_head_node_cut_after_script():
     assert unity._head_node(TypeTreeNode(0, "X", "Base", -1, 1, m_Children=kids[:2])) is None
 
 
+def test_script_class_missing_script_is_none():
+    kids = [TypeTreeNode(1, t, n, 0, 0) for t, n in (("PPtr<GameObject>", "m_GameObject"), ("UInt8", "m_Enabled"),
+                                                       ("PPtr<MonoScript>", "m_Script"))]
+    node = TypeTreeNode(0, "MonoBehaviour", "Base", -1, 1, m_Children=kids)
+    null = {"m_FileID": 0, "m_PathID": 0}
+    obj = SimpleNamespace(_get_typetree_node=lambda: node,
+                          read_typetree=lambda *a, **k: {"m_GameObject": null, "m_Enabled": 1, "m_Script": null})
+    assert unity.script_class(obj) is None
+    whole = SimpleNamespace(_get_typetree_node=lambda: None,
+                            read=lambda: SimpleNamespace(m_Script=SimpleNamespace(m_PathID=0)))
+    assert unity.script_class(whole) is None
+
+
 # ---------------------------------------------------------------- typetree values
 def ref_value(ex, owner, v):
     if unity.is_pptr(v):